This invention relates to image forming screens for optical equipment, and more particularly to a method and apparatus for increasing the brightness and quality of the image formed on such screens while providing uniform illumination over the image area.
Present professional long film roll cameras are of the twin lens reflex type having a ground glass image forming viewing screen positioned behind a viewing lens in the upper portion of the camera and a film image forming or taking lens in the lower portion of the camera. Typically, a 100 foot roll of film will produce from 500 to 1,800 frames per rolls, depending upon the negative size, since such cameras are used to photograph a multitude of photographs each day. Generally, in studio and similar posed photography environments the posing lighting may consist of 150 watts in a space of 15 feet by 15 feet with the camera placed from 6 to 20 feet from the subject. Furnishings under these conditions are usually dark and textured to minimize reflections. The photographer is thus composing by looking at an extremely dim image approximately 2 inches by 1+3/4 inches on the viewing screen. In addition to this dim environment the photographer may have to photograph at other locations such as store windows, advertising displays, and similar environments where the bright back lights may introduce reflections in the viewer optics or expose his eyes to lighting contrasts.
The procedure of composing, focusing, and making technical and artistic judgements on some 500 to 700 subjects daily imposes a strain on the eyes and visual perception of the photographer. Inasmuch as the results of a days work may not be seen for two weeks, the economic losses due to any poorly focused photos can be significant.
Similar visual eye strain and loss of perception and acuity result in other optical systems in which there is a rear projection of an image upon a screen such as opaque projectors, micro film projectors, movie editor machines and consoles, microscope projectors and many other types of cameras and other back projection screen devices.